1. Technical Field of the Invention
This invention relates generally to mixed signal processing and more particularly to audio signal processing.
2. Description of Related Art
Headphones are known to provide an improved listening experience for listening to a variety of audio sources. For example, headphones may be used in commercial settings (e.g., recording studio, audio laboratories, etc.) to listen to audio content (e.g., music, audio signals, voice signals, etc.) with little to no interference from external sources (e.g., background noise). As another example, headphones may be used in recreational settings (e.g., at home, at the office, etc.) to listen to audio output by a digital audio player (e.g., MP3), an AM/FM radio, a television, a CD player, a DVD player, etc. with reduced interference from external sources and/or for private listening.
In general, a headphone includes one or more speakers (typically two) that can be held closely to the user's ears and circuitry for connecting to an audio source. For example, ear-bud headphones are held close to the user's ears by a pressure fit and include a male audio jack for connecting to a source. As other examples, the headphone may have an ear-cup or on-ear design that fit over the ears; may have a circumaural or full size design that completely surround the ears; or may have a supra-aural design that are light-weight and sits on the ears.
Headsets are known to provide “hands-free” operation of a communication device (e.g., landline telephone, cellular telephone, voice over IP telephone, two-way radio, etc.). As is also known, a headset is essentially a headphone with one or more microphones. In this regard, a headset provides the listening features of a headset with the added ability to transmit voice and/or other audio signals.
To further improve the listening experience, some headphones and/or headsets include noise cancelling circuitry. As is known, the noise cancelling circuitry includes one or more omni-directional microphones to receive noise that is proximal to user but does not receive noise that is further away. The noise received by the microphone may be filtered, amplified, and phase inverted to cause a reduction in proximal noise to the user. An audio signal may also be combined with the noise cancelling circuitry in a manner that allows the system to reproduce the audio signal. In this manner, the audio signal provided to the speaker(s) of the headset or headphone includes the desired audio signal and an inverted version of the noise to be suppressed.
While noise cancelling headsets and/or headphones work well in many situations where the noise level is modest (e.g., on an airplane, in a building, etc.), as the noise level increases, the noise cancelling circuitry becomes unstable and may increase the noise level. For instance, when headsets and/or headphones are used in extremely loud environments (e.g., helicopters, jets, blasting sites (e.g., demolition, military battles, etc.), at a race track, etc.) conventional noise cancelling circuitry is inadequate and a more robust noise cancellation technique is needed. Even with the more robust noise cancellation circuitry, many persons who are regularly exposed to extremely loud environments experience noise-induced hearing loss.
Another issue for headsets/headphones in loud environments is to allow desired surrounding environmental audio signals to be heard while suppressing the undesired noise. This issue may be referred to as localization. For instance, a user may be involved in a communication, thus the incoming voice signals are desired and the background noise (e.g., wind, engine noise, etc.) and loud transient noise (e.g., a gun shot, a engine back-firing, etc.) are undesired. Thus, the desired audio signals should pass through to the speakers (i.e., hear-through) while the background noise and transient noise should be suppressed.
While many headsets/headphones designed for extremely loud environments address one or more of the above issues, they do not address some of the other issues. For example, a headset/headphone may address the loud background noises but does not handle the loud transient noises well or does not provide an adequate level of hear-through considering the hearing profile of the listener.
Therefore, a need exists for a hearing system that functions well in extremely loud environments by addressing the localization problem to provide hear-through, addressing hearing loss, suppressing loud transient noises, and/or suppressing loud background noises.